Transgender men, who were assigned female sex at birth and have transitioned into their male sex, experience greater insulin sensitivity after undergoing a year of hormone therapy, according to results of a new study.

The Belgium study found that the converse happens to insulin sensitivity in transgender women when they have been taking the reassignment hormone therapy for a year to transition from male to female sex.

The study involved 55 transgender women and 35 transgender men. Average age was 26 years old for the transgender men and 34 years old for the transgender women.

At the start of the trial, and before they began taking their medication, all the participants had various health data measured such as their height, weight, lean mass, waist circumference, fasting plasma glucose and fasting insulin. A year after they had started taking their hormone therapy, all the volunteers had the same measurements taken again.

The results found that transgender men, undergoing male hormone therapy, experienced an increase in insulin sensitivity, whereas the transgender women, who underwent female hormone therapy, experienced a decrease in insulin sensitivity.

The finding could have clinical implications as the results suggest that transgender men may be at greater risk of developing type 2 diabetes. Further research is needed to confirm the findings and to investigate the implications.

Professor Samyah Shadid, of Ghent University Hospital in Belgium, said: “To what extent these observations are reproducible has yet to be determined; until then, it might be advisable to monitor insulin sensitivity parameters regularly in transgender people after gender-affirming hormone therapy.”

In terms of body weight, the researchers found the average body weight among the transgender men started out at 63.1kg and increased to 65.9kg after a year of hormone therapy. There was no significant change in body weight among the transgender women.

Body weight change may be ambiguous as there are different permutations possible in terms of increases and decreases in muscle and fat mass. Previous research has shown hormone therapy for transgender men to tend to increase lean body mass and decrease fat mass. However, the current study did not investigate this aspect.

The researchers concluded: “Even though not all parameters and markers changed significantly, nor into the same direction, the fact that the changes in insulin sensitivity largely tended toward opposite directions in both groups suggests that, at least in our study cohort, people were more insulin sensitive under male than under female hormone exposition.”

The findings have been published in the Diabetes Care journal.

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